Efficient Intramolecular Hydroalkoxylation of Unactivated Alkenols Mediated by Recyclable Lanthanide Triflate Ionic Liquids: Scope and Mechanism

Migratory insertion of alkenes into metal-oxygen and metal-nitrogen bonds

The insertion of an unsaturated ligand into a M-C or M-H bond proceeds through migratory insertion, a fundamental organometallic reaction. Recent literature documents evidence of the migratory insertion of alkenes into an M-O and M-N bonds for alkene alkoxylation and alkene amination reactions, respectively. Herein we provide an overview of the literature and a perspective on how these recent experiments relate to classic experiments on C-O and C-N bond formation with alkene complexes of the late transition metals.

Experimental and theoretical studies on the bismuth-triflate-catalysed cycloisomerisation of 1,6,10-trienes and aryl polyenes

Cycloisomerisation of polyenes such as diethyl geranylprenylmalonate [(E)-1 a], diethyl geranylphenylmalonate [(E)-2 a] and diethyl cinnamylgeranylmalonate [(E,E)-3 a] catalysed by bismuth triflate was studied from experimental and theoretical viewpoints. Several intermediates were isolated and characterised, and calculated transition-state structures are proposed for the three reactions. The diastereoselectivity observed during the reaction of (E)- or (Z)-2 a in favour of the formation of trans-fused bicyclic products is discussed in detail. The nature of the active catalytic species derived from bismuth triflate was also investigated, and the formation of a hybrid Lewis acid/Brønsted acid catalyst with water molecules is proposed, supported by experimental and theoretical data.

A cycloisomerization/Friedel-Crafts alkylation strategy for the synthesis of pyrano[3,4-b]indoles

The synthesis of pyrano[3,4-b]indoles is described. The reaction sequence involves Sonogashira coupling of dihydropyran propargyl ether scaffolds with iodoanilines to afford intermediate indoles. Lewis acid-catalyzed ionization of the dihydropyrans, followed by intramolecular C3 alkylation of the indole, provides the title compounds.

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

New gold-catalyzed methods using the β-lactam scaffold have been recently developed for the synthesis of different sized heterocycles. This overview focuses on heterocyclization reactions of allenic and alkynic β-lactams which rely on the activation of the allene and alkyne component. The mechanism as well as the regio- and stereoselectivity of the cyclizations are also discussed.

Intramolecular hydroalkoxylation in Brønsted acidic ionic liquids and its application to the synthesis of (±)-centrolobine

The SO(3)H-tethered imidazolium and triazolium salts, nonvolatile and recyclable Brønsted acidic ionic liquids, efficiently mediate intramolecular hydroalkoxylations of alkenyl alcohols. They have been successfully employed in the synthesis of (±)-centrolobine.